Rationale and Hypothesis:
Pulmonary arterial hypertension (PAH) is a fatal disease characterised by the narrowing of small pulmonary arteries through sustained vasoconstriction and abnormal vascular remodelling. The adenosine diphosphate (ADP) receptor P2Y12 has been suggested to play a role in vasoconstriction and vascular remodelling in other diseases; we therefore hypothesised P2Y12 blockade may be beneficial in PAH.
P2RY12 mRNA expression in healthy and PAH patients’ pulmonary artery smooth muscle cells (PASMCs) was determined by qPCR. The effect of ADP on iloprost-induced vasodilator stimulated phosphoprotein (VASP) phosphorylation was quantified by In Cell Western and the phenotypic effects of P2Y12/ADP were determined by proliferation and migration assays in healthy and PAH PASMCs. Monocrotaline (MCT) (60 mg/kg) treated rats were randomised to receive the P2Y12 inhibitor, clopidogrel (50 mg/kg) or placebo by daily oral gavage. Treatment was commenced for 2 weeks, 2 weeks following MCT injection prior to echocardiography, cardiac catherisation and tissue harvest. Pharmacodynamic effects of clopidogrel were quantified using light transmittance platelet aggregometry. Lung tissue was histologically assessed for vascular muscularisation.
P2RY12 expression was increased in PAH PASMCs compared to healthy controls (relative quantitative (RQ) (5.9 ± 0.9 vs 1.1 ± 0.06, n=4-9, p<0.01). ADP induced almost 30% increase in PASMC migration compared to unstimulated control (n=5, p <0.01). Clopidogrel treatment of MCT rats significantly inhibited 10 μmol/L ADP-induced platelet aggregation compared to placebo animals (76.7 ± 13.2 % vs 5 ± 2 %; n=3-5, p<0.01). P2Y12 inhibition by clopidogrel reduced pulmonary vascular remodelling in the Mct rat (n=4-8, p <0.05) but had no effect on haemodynamics after 2 weeks treatment.
Further work is required to determine if longer treatment with a P2Y12 inhibitor would have a more beneficial therapeutic effect